It has been established that alkylpyrazines are natural components of tobacco smoke, and that they are contributors to tobacco smoke flavor [A. Baggett et al J. Chromatog. 97, 79 (1974)] 2-Isopropenylpyrazine has been identified as a tobacco flavorant constituent of burley tobacco [E. Demole et al, Helv. Chem. Acta, 55, 1866 (1972)].
Patents which disclose the addition of various pyrazine compounds to tobacco and foodstuffs as a means of providing flavor or flavor enhancement include U.S. Pat. Nos. 3,684,809; 3,705,158; 3,754,934; 3,764,349; 3,767,426; and 3,881,025.
Alkylpyridines also have been found to be useful tobacco additives. U.S. Pat. No. 3,625,224 describes the use of methylpyridines, ethylpyridines and various dialkylpyridines as tobacco additives. U.S. Pat. No. 3,381,691 discloses 2-methyl-5-isopropylpyridine as a tobacco additive.
It is characteristic of pyrazine and pyridine and other heteroaromatic derivatives employed as tobacco flavorants in the prior art that the respective derivatives have the disadvantage of both high volatility and low odor threshold. Both of these properties significantly restrict the extent that these heteroaromatic derivatives can be utilized as flavorants in tobacco compositions. A quantity of a pyrazine or pyridine derivative in a tobacco composition sufficient to have a noticeable effect in low delivery cigarettes causes a marked pack aroma.
U.S. Pat. No. 4,259,969 endeavors to overcome some of the disadvantages of the above-described flavorant technology. The patent describes smoking composition flavorant-release additives such as 2,3-dihydroxy-2,3-dimethyl-1,4-bis(3,5,6-trimethyl-2-pyrazinyl)butane. Under smoking conditions substituted pyrazine pyrolysis products are released which enhance the flavor of the mainstream smoke and improve the aroma of the sidestream smoke.
U.S. Pat. No. 4,312,368 and related U.S. Pat. No. 4,479,003 describe heterocyclic-hydroxy-substituted alkanoate flavorant additives such as ethyl 2-(2-butyl)-3-hydroxy-3-methyl-3-(3-pyridyl)propionate, which under normal smoking conditions pyrolyzes into components which contribute enhanced flavor and aroma to the smoke streams. U.S. Pat. No. 4,872,918 describes heteroaromatic ester flavorant-release additives such as methyl 3,5,6-trimethyl-2-pyrazineacetate, which is adapted to release tetramethylpyrazine flavorant under cigarette smoking conditions.
There is continuing research effort to develop improved smoking compositions which contain a new and efficient low volatility flavorant-release additive, and which generate mainstream smoke with flavorant-enhanced taste and character under smoking conditions.
Accordingly, it is an object of this invention to provide smoking compositions having incorporated therein a flavorant component which is characterized by lack of mobility and/or volatility at ambient temperature.
It is another object of this invention to provide smoking compositions having incorporated therein a flavorant-release additive which under normal smoking conditions yields pyrolysis constituents which impart improved flavor to mainstream smoke and improved aroma to sidestream smoke.
It is another object of this invention to provide novel oxalate compounds of low volatility which are adapted to be incorporated into cigarette fillers, and which under normal smoking conditions release a volatile heteroaromatic flavorant constituent into cigarette smoke.
It is a further object of this invention to provide a novel process for producing substituted heteroaromatic compounds.
Other objects and advantages of the present invention shall become apparent from the following description and examples.